* Baby powder is used to absorb moisture and prevent chafing. It has no properties that would affect muscle growth or fat storage.
* Vaseline (petroleum jelly) is an occlusive moisturizer. It can help to hydrate and protect the skin, but it will not increase the size of your butt.
The size of your butt is determined by genetics, muscle mass, and body fat distribution. To increase the size of your butt, you would need to focus on exercises that target the gluteal muscles (squats, lunges, hip thrusts) and potentially increase your overall body fat percentage through a calorie surplus.